For insect control, it is customary to produce polymeric fibres or other polymeric articles by incorporating insecticides in the polymeric matrix of the articles and let the insecticide migrate from the bulk of the matrix to the surface of the matrix for uptake of the insecticide by insects that contact the surface. Control of migration of insecticides is of high interest, because such products, often, are intended for long term use against insects, why the migration should be fast enough for replenishing insecticide that is lost from the surface but also slow enough to guarantee a long, efficient lifetime of the article. For this reason, it is known to include migration enhancers or migration reducers in the matrix.
Adjustment of the migration is discussed in International patent application WO2008/004711 by Sumitomo concerning mainly the bleed coefficient, which is determined by a large number of factors including pigments. In the application WO2003/063587 by Vestergaard Frandsen, Carbon Black is mentioned in connection with migration of insecticides, and in Battelle's U.S. Pat. No. 5,019,998, simulation models are disclosed on Carbon Black's influence on migration. Dow's U.S. Pat. No. 4,680,328 discloses an insecticidal (chlorpyrifos) polyethylene (PE) composition for a cable with Carbon Black as compatibility additive which increases the retention time, as it is illustrated in Table II of this application when comparing sample 2 and 3, which are identical apart from a content of 2.6% carbon black (see Table I).
In the International patent application WO2008/098572 by Vestergaard Frandsen, a discussion is disclosed on migration inhibitors and migration promoters for insecticides and synergists, where it is mentioned that different substances may work differently on insecticides when compared to the effect on synergists. Some promoters or inhibitors may work more or less on deltamethrin (DM) than on piperonyl butoxide (PBO) by which the migration speed of these two components can be adjusted relatively.
The influence of different types of migration controlling agents depends on the type of agent and on the type of insecticide or synergist. Some agents are believed to take up the insecticide or synergist and act as a carrier therefore. Especially, porous particles are believed to have this property. Although Carbon Black is known as a carrier for insecticides with a retarding effect, not all porous particles necessarily are migration retarding. Interesting in this connection is the fact that kaolin, which often is regarded as a filler and carrier, for example as disclosed in WO2008/128896. Kaolin is disclosed as being migration increasing in the application WO2003/063587 by Vestergaard Frandsen. Thus, apparently, not all types of fillers that potentially can take up insecticide and synergists, like PBO, are migration retarding.
Some migration controlling agents, such as colorants, dyes, or pigments, are believed to modify the crystalline structure of the polymer, for example as discussed in Microban's U.S. Pat. No. 6,979,455. Thus, the control of migration is generally a complex process. Further, to the complexity of the retention process adds the influence of stretching, not only due to the crystallinity that changes during stretching, but also due to the formation of microvoids, as it is discussed in Sumitomo's EP582823 concerning release control.
In general, the control of the migration and retention of insecticides and synergists in polymeric matrices is of utmost concern and studies are ongoing because there is a general desire for improvements.